Magnetic transmit antennas are typically configured as loops of wire having a modulated current driven through them. The higher the current at the transmitted frequencies, the greater the strength of the magnetic field and, hence, the greater the transmission range of the antenna. Conventional transmit antenna designs often use a power amplifier coupled directly to the antenna, along with a tuning capacitor to cause the antenna loop to be resonant at the transmission frequency. Loop resonance is one way to increase the current and hence the magnetic field strength of the transmit antenna. However, inducing resonance in the loop antenna may undesirably generate high voltages at the resonant frequency. Such high voltages can be in the range of 1,000 to 4,000 volts, for example. These voltages can create electrical arcs that could ignite explosive gasses within the transmitter's operational environment (e.g. a coal mine) and/or cause other undesirable effects.
On the other hand, if the additional tuning circuitry is not used in conjunction with a power amplifier directly coupled to the magnetic transmit antenna so as to cause resonance within the loop antenna (and thereby increase the magnetic field strength) then a much more powerful amplifier must be used in order to provide a substantial drive current to the loop antenna for most practical applications. For example, if a loop antenna presented a load impedance of 2 ohms, and if 100 amperes of current is needed in each loop of antenna wire for a sufficient magnetic field strength for a given application, then the amplifier would be required to provide about 200 volts of drive voltage at 100 amperes (i.e. 20,000 Watts or 20 KW). Such high power amplifiers are extremely costly, heavy and generally impractical to implement in most environments. Moreover, such a high power amplifier would severely drain a portable battery, present both a large and weighty mass element, and further generate significant heat losses. Such undesirable effects tend to preclude implementation of such a structure, particularly in environments requiring portable operations. Alternative mechanisms for increasing transmission range of magnetic loop transmit antennas is desired.